Rename from Simfony to SimplicityHL

[kiarafbickers]

Changed all mentions of Simfony to SimplicityHL in docs, comments, urls, and text. No code, filenames, or logic was changed, just text!

[uncomputable]

The crate needs to be renamed on crates.io: https://crates.io/crates/simfony

[apoelstra]

@kiarafbickers can you add a commit which updates the README.md to add a bold note at the top saying the crate has been renamed to SimplicityHL and is now available at https://crates.io/crates/SimplicityHL ? And bump the version number to 0.1.1 so we can release a new version with that text visible.

That link is a 404 right now but we will do a followup PR to re-release the crate as SimplicityHL.

Also the CI failure on this PR is real -- you need to run cargo fmt on this crate after any changes.

[apoelstra]

@kiarafbickers what is the status of this?